.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines
.\" Copyright (c) 2020      Google, LLC. All rights reserved.
.\" $COPYRIGHT$
.TH MPI_Comm_set_attr 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
.SH NAME
\fBMPI_Comm_set_attr\fP \- Stores attribute value associated with a key.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Comm_set_attr(MPI_Comm \fIcomm\fP, int \fIcomm_keyval\fP, void *\fIattribute_val\fP)

.fi
.SH Fortran Syntax (see FORTRAN 77 NOTES)
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_COMM_SET_ATTR(\fICOMM, COMM_KEYVAL, ATTRIBUTE_VAL, IERROR\fP)
	INTEGER	\fICOMM, COMM_KEYVAL, IERROR \fP
	INTEGER(KIND=MPI_ADDRESS_KIND) \fIATTRIBUTE_VAL\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Comm_set_attr(\fIcomm\fP, \fIcomm_keyval\fP, \fIattribute_val\fP, \fIierror\fP)
	TYPE(MPI_Comm), INTENT(IN) :: \fIcomm\fP
	INTEGER, INTENT(IN) :: \fIcomm_keyval\fP
	INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) :: \fIattribute_val\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH INPUT/OUTPUT PARAMETER
.ft R
.TP 1i
comm
Communicator from which attribute will be attached (handle).

.SH INPUT PARAMETERS
.ft R
.TP 1i
comm_keyval
Key value (integer).
.TP 1i
attribute_val
Attribute value.

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_Comm_set_attr stores the stipulated attribute value \fIattribute_val\fP for subsequent retrieval by MPI_Comm_get_attr. If the value is already present, then the outcome is as if MPI_Comm_delete_attr was first called to delete the previous value (and the callback function delete_fn was executed), and a new value was next stored. The call is erroneous if there is no key with value \fIcomm_keyval\fP; in particular MPI_KEYVAL_INVALID is an erroneous key value. The call will fail if the delete_fn function returned an error code other than MPI_SUCCESS.
.sp
This function replaces MPI_Attr_put, the use of which is deprecated. The C binding is identical. The Fortran binding differs in that \fIattribute_val\fP is an address-sized integer.

.SH FORTRAN 77 NOTES
.ft R
The MPI standard prescribes portable Fortran syntax for
the \fIATTRIBUTE_VAL\fP argument only for Fortran 90. Sun FORTRAN 77
users may use the non-portable syntax
.sp
.nf
     INTEGER*MPI_ADDRESS_KIND \fIATTRIBUTE_VAL\fP
.fi
.sp
where MPI_ADDRESS_KIND is a constant defined in mpif.h
and gives the length of the declared integer in bytes.

.SH NOTES
.ft R
Values of the permanent attributes MPI_TAG_UB, MPI_HOST,
MPI_IO, and MPI_WTIME_IS_GLOBAL may not be changed.
.sp
The type of the attribute value depends on whether C or Fortran is being used. In C, an attribute value is a pointer (void *); in Fortran, it is a single, address-size integer system for which a pointer does not fit in an integer.
.sp
If an attribute is already present, the delete function (specified when the corresponding keyval was created) will be called.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

